In the 1920's, a series of experiments were conducted on human sight which led to the specification of what is called the CIE xyz color space. This color space contains all perceivable colors (or gamut) that the human eye can detect. Most computer monitors, televisions and other similar devices use an RGB (red/green/blue) color space model, which is a subset of the CIE xyz color space due to the fact that these devices cannot recreate every possible human perceptible color. By combining different values of three primary colors (red, green, and blue), any color within the RGB color space gamut can be created. Not to be overlooked, white is the combination of all three primary colors and black is the absence of any color.
Most electronic displays in use today represent color with 8 bits of precision; that is, the intensity of each color channel (red, green, or blue) can be represented as an 8-bit number (0-255 decimal, or 0x00-0xFF hex). A modern electronic display is capable of producing on the order of 16.7 million distinct colors using this method.
In order to transmit data through a display device, the sequential presentation of colors representing encoded data must be presented as a video stream, or alternatively, presented via dedicated software to mimic a video stream—at a frame rate that can be reproduced reliably on a given display device. The refresh rate of a given display device will dictate the highest achievable video frame rate, with 60 Hz being a common baseline on desktop computer displays. 15-30 frames per second video can be reliably displayed on such devices, meaning that raw data transfer rates on the order of a few tens to a few hundred bits per second could be achieved assuming a data encoding density of 3 to 8 bits per distinct color. By increasing either or both data encoding density and number of frames displayed per second, the data transfer rate can be increased accordingly.
Many different electronic sensors are capable of detecting colors, and most work off of the same principle—a photo-sensitive device behind one or more color filters. For example, an imaging sensor that you would find in a digital camera consists of thousands (or millions) of pixels, with each individual pixel being behind a red, green, or blue color filter. By counting the number of photons hitting the sensor over a given period of time (integration), a relative digital count of each red, green and blue pixel can be ascertained—the combination of which would yield a digital representation of the sensed color.
Other than common multi-pixel imaging sensors, there also exists a class of device which is basically a dedicated “single-pixel” color sensor; that is, a sensor that is only able to detect a single color at a time. An example of such a sensor is the TCS3414 digital color sensor manufactured by Texas Advanced Optoelectronic Solutions (TAOS). Similar sensors are also manufactured by Avago Technologies as well as others. These are generally available in very small packages (approximately 2 mm×2 mm square) and at very low price points (a few dollars each). These sensors are used in industry for a number of purposes including industrial process control, instrumentation (colorimeters), consumer toys, etc.
Most electronic sensors described above do not respond equally to a given primary (red, green or blue) color; that is, the blue channel in such sensors is generally less sensitive than the red and green channels, while the green channel is less sensitive than the red channel. This unequal channel response, together with potential inconsistent repeatability and overall sensitivity characteristics can create challenges if such single pixel sensors were to be used to sense and decode a stream of encoded “video” data. What is needed is a novel method considering such challenges inherent in the single pixel sensor that will allow the sensor to operate at relatively high frequencies of 15-30 frames per second or more to decode a single-color “video stream”, and effectively to become a single-pixel video camera.